This invention relates to sewing machines and, more particularly, to electronic controls for positioning stitch forming instrumentalities thereof.
Sewing machines are known in the prior art wherein the positional coordinates for successive stitch penetrations are stored in a memory having addressable locations corresponding to a plurality of operator selectable patterns. In particular, such known sewing machines include logic circuitry which is used to select and release the stitch pattern information stored in the memory in timed relation with the operation of the sewing machine. Digital information from the memory is converted to positional analog signals which control closed loop servo systems including moving coil linear actuators directly controlling the position of conventional stitch forming instrumentalities of the sewing machine to reproduce a pattern of stitches corresponding to the selected stitch information. The timing signals for operating the logic circuitry are generally derived from a timing pulse generator coupled to the horizontal armshaft of the sewing machine. Accordingly, the timing signals are generated in synchronism with the operation of the sewing machine at fixed points relative to each operating cycle of the sewing machine and the spacing between the timing signals is dependent upon the speed of operation of the sewing machine. Thus, a faster sewing machine speed causes the timing signals to be spaced closer together than a slower sewing machine speed. In general, the response time of the servo system including the linear actuator is sufficiently fast to properly position the stitch forming instrumentalities between stitches at any speed within the normal range of sewing machine speeds. However, under certain circumstances, when the sewing machine is operating above some threshold speed, there may be insufficient time to properly position a stitch forming instrumentality if the mechanically synchronized timing pulses are utilized. It is therefore an object of the present invention to insure that the stitch forming instrumentalities are properly positioned at all operating speeds of the sewing machine.